The paper examines chemical and structural modifications effected in the nanosecond UV ablation of polymers. For the study of the photochemical effects, laser-induced fluorescence LIF is employed for monitoring photoproduct formation in the substrate in the UV ablation of PMMA films doped with the photosensitive iodonaphthalene (NapI). Photoproduct formation in the ablative regime is observed to continue for much longer (approximate tomus), following the pump laser pulses than in the case of irradiation below the threshold (approximate tomus). Furthermore, formation of bi-aryl compounds (Nap(2) and perylene) is observed upon ablation at 308, 248 and 193 nm. The implications of these observations for the reactivity during ablation are discussed. As for the examination of the photomechanical effects, holographic interferometry is employed for the characterisation of the structural modifications that are induced around a considerable distance from the irradiation spot. The examination demonstrates the formation of defects that are not observed in the irradiation at low laser fluences. (C) 2002 Elsevier Science B.V. All rights reserved.